Conventionally, 4-hydroxy-butanal 2-hydroxy-tetrahydrofuran, and 2-methyl-3-hydroxypropanal are industrially prepared by hydroformylating allyl alcohol, carbon monoxide, and hydrogen in the presence of rhodium as a catalyst The reactions of the conventional processes are shown as follows: ##STR1##
4-hydroxy-butanal and 2-hydroxy-tetrahydrofuran can be used for producing 1,4-butanediol through hydrogenation while 2-methyl-3-hydroxypropanal can be used for producing 2-methyl-1,3-propanediol through hydrogenation. The reactions thereof are shown as follows: ##STR2##
The hydrogenation of 4-hydroxy-butanal and 2-methyl-3-hydroxypropanal is subject to hydrogenation of carbonyl group. Presently, the catalyst used in the process of hydrogenation of carbonyl group is selected from precious metals including palladium, which is disclosed in Biochemistry Journal, 1943, Vol. 37, p.726; platinum which is disclosed in Journal of American Chemical Society, 1948, Vol. 70, p.664; ruthenium, which is disclosed in U.S. Pat. No. 3,144,490; rhenium, which is disclosed in Journal of Organic Chemistry, 1959, Vol. 24, p.1847; copper chromite, which is disclosed in Industrial and Engineering Chemistry, 1946, Vol. 38, p.251; copper, which is disclosed in British Patent No. 659,981; nickel, which is disclosed in Journal of Chemical Society, Japan, Industrial Chemistry Section, 1943, Vol. 46, p.901; Raney nickel, which is disclosed in Journal of American Chemical Society, 1948, Vol. 70, p.695; Raney cobalt, which is disclosed in Journal of Applied Chemistry, 1958, Vol. 8, p.492; and so on.
Through long-term experiments, it has been found by the inventors that the hydrogenations of 4-hydroxy-butanal, 2-hydroxy-tetrahydrofuran, and 2-methyl-3-hydroxypropanal differ from that of other carbonyl groups. For instance, the use of palladium or zinc copper oxide as catalyst shows almost no reaction activity; and the use of ruthenium or copper chromite as catalyst shows only relatively low reaction activity to the hydrogenation which provides little utilization value. Only nickel and Raney nickel provide higher reaction activity to the hydrogenation. However, it has been subsequently found a drawback to the use of nickel or Raney nickel as catalyst in the aforementioned hydrogenation process in that their reaction activity rapidly decay after repetitive uses. More specifically, after batchwise repetitive uses exceeding 33 batches or continuous use exceeding 30 hours, their reaction activity significantly decreases to a low level that can't practically be used further. Accordingly, the use of nickel or Raney nickel as catalyst in the hydrogenation process for producing 1,4-butanediol, 2-methyl-1,3-propanediol from 4-hydroxy-butanal, 2-hydroxy-tetrahydrofuran, and 2-methyl-3-hydroxypropanal is still not a practical approach in the chemical industry.